The invention concerns a brake device for a linear guide comprising a carrier body which is movable on a guide rail and incorporates brake shoes which act on the guide rail, and a brake piston which is arranged for displacement by a pressure medium in a brake cylinder of the carrier body, the brake device further comprising an energy reservoir in form of a compression spring which acts on the pressure medium that is limited by the brake piston.
Linear guides are used, among other things, in machine tools with high speed drives, linear platens and laser machining tools. In a brake device for a linear guide known from DE-GM 295 05 080, the braking or locking force is provided by the pressure medium, for example, a hydraulic pressure medium such as oil. However, from the standpoint of safety, this linear guide is inadequate because if there is an unintentional drop of pressure in the pressure medium, the carrier body can no longer be braked or locked on the guide rail.
The object of the invention is to create a linear guide whose carrier body can be braked and locked mechanically in a reliable manner on the guide rail in emergencies such as pressure medium failure.
The invention achieves this object by the fact that a piston/cylinder assembly is arranged between the compression spring and the brake piston, said assembly comprising a unitary control element comprising a displaceable, larger diameter control piston arranged in a control pressure chamber to act on the compression spring and a displaceable, smaller diameter high pressure piston arranged in a high pressure chamber to act on the brake piston, a pressure connection for supply of pressure medium into the control pressure chamber being disposed on the carrier body. This results in the formation of a hydro-mechanical emergency braking system whose braking energy is provided by the energy reservoir situated in the brake device.
The compression spring which acts as the energy reservoir may be a coil compression spring, a disc spring or spring washers. However, a gas pressure reservoir may also be used for this purpose.
The control piston, the high pressure piston and the compression spring can have a common longitudinal axis extending in the guide direction of the carrier body. By this, a large potential stroke of the high pressure piston which is desirable for safety reasons is obtained.
A compensating reservoir for the pressure medium may be arranged in or on the carrier body and connected by a pressure medium duct to the high pressure chamber and the brake cylinder. Such a compensating reservoir makes it possible to compensate for wear of the brake shoes and leakage losses by a refilling of the pressure medium. It is advantageous in this case to arrange a one-way valve between the compensating reservoir and the pressure medium duct.
Advantageously, the compensating reservoir may have a cylindric configuration and comprise a displaceable compensating piston for the variable pressure medium volume of the reservoir.